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SubjectRE: [PATCH v2] kunit: fix failure to build without printk
Date
> -----Original Message-----
> From: Brendan Higgins
>
> On Fri, Aug 30, 2019 at 11:22:43PM +0000, Tim.Bird@sony.com wrote:
> > > -----Original Message-----
> > > From: Brendan Higgins
> > >
> > > On Fri, Aug 30, 2019 at 3:46 PM Joe Perches <joe@perches.com> wrote:
> > > >
> > > > On Fri, 2019-08-30 at 21:58 +0000, Tim.Bird@sony.com wrote:
> > > > > > From: Joe Perches
> > > > []
> > > > > IMHO %pV should be avoided if possible. Just because people are
> > > > > doing it doesn't mean it should be used when it is not necessary.
> > > >
> > > > Well, as the guy that created %pV, I of course
> > > > have a different opinion.
> > > >
> > > > > > then wouldn't it be easier to pass in the
> > > > > > > kernel level as a separate parameter and then strip off all printk
> > > > > > > headers like this:
> > > > > >
> > > > > > Depends on whether or not you care for overall
> > > > > > object size. Consolidated formats with the
> > > > > > embedded KERN_<LEVEL> like suggested are smaller
> > > > > > overall object size.
> > > > >
> > > > > This is an argument I can agree with. I'm generally in favor of
> > > > > things that lessen kernel size creep. :-)
> > > >
> > > > As am I.
> > >
> > > Sorry, to be clear, we are talking about the object size penalty due
> > > to adding a single parameter to a function. Is that right?
> >
> > Not exactly. The argument is that pre-pending the different KERN_LEVEL
> > strings onto format strings can result in several versions of nearly identical
> strings
> > being compiled into the object file. By parameterizing this (that is, adding
> > '%s' into the format string, and putting the level into the string as an
> argument),
> > it prevents this duplication of format strings.
> >
> > I haven't seen the data on duplication of format strings, and how much this
> > affects it, but little things can add up. Whether it matters in this case
> depends
> > on whether the format strings that kunit uses are also used elsewhere in
> the kernel,
> > and whether these same format strings are used with multiple kernel
> message levels.
> > -- Tim
>
> I thought this portion of the discussion was about whether Joe's version
> of kunit_printk was better or my critique of his version of kunit_printk:
>
> Joe's:
> > > > > -void kunit_printk(const char *level,
> > > > > - const struct kunit *test,
> > > > > - const char *fmt, ...)
> > > > > +void kunit_printk(const struct kunit *test, const char *fmt, ...)
> > > > > {
> > > > > + char lvl[PRINTK_MAX_SINGLE_HEADER_LEN + 1] = "\0";
> > > > > struct va_format vaf;
> > > > > va_list args;
> > > > > + int kern_level;
> > > > >
> > > > > va_start(args, fmt);
> > > > >
> > > > > + while ((kern_level = printk_get_level(fmt)) != 0) {
> > > > > + size_t size = printk_skip_level(fmt) - fmt;
> > > > > +
> > > > > + if (kern_level >= '0' && kern_level <= '7') {
> > > > > + memcpy(lvl, fmt, size);
> > > > > + lvl[size] = '\0';
> > > > > + }
> > > > > + fmt += size;
> > > > > + }
> > > > > +
> > > > > vaf.fmt = fmt;
> > > > > vaf.va = &args;
> > > > >
> > > > > - kunit_vprintk(test, level, &vaf);
> > > > > + printk("%s\t# %s %pV\n", lvl, test->name, &vaf);
> > > > >
> > > > > va_end(args);
> > > > > }
>
> Mine:
> > void kunit_printk(const char *level,
> > const struct kunit *test,
> > const char *fmt, ...)
> > {
> > struct va_format vaf;
> > va_list args;
> >
> > va_start(args, fmt);
> >
> > + fmt = printk_skip_headers(fmt);
> > +
> > vaf.fmt = fmt;
> > vaf.va = &args;
> >
> > - kunit_vprintk(test, level, &vaf);
> > + printk("%s\t# %s %pV\n", level, test->name, &vaf);
> >
> > va_end(args);
> > }
>
> I thought you and Joe were arguing that "Joe's" resulted in a smaller
> object size than "Mine" (not to be confused with the actual patch I
> presented here, which is what Sergey suggested I do on a different
> thread).
>
> I really don't feel strongly about what Sergey suggested I do (which is
> what this patch originally introduced), versus, what Joe suggested,
> versus what I suggested in response to Joe (or any of the things
> suggested on other threads). I just want to pick one, fix the breakage
> in linux-next, and move on with my life.

When in doubt, do what the sub-system maintainer says. I'd go
with Sergey's suggestion. Maintainers often are juggling a host
of issues, and weighing new features and usages of their system
against their long-term plans for their sub-system. Sometimes
they have time to communicate all the intricacies of their
counter-proposals, and sometimes not.

But they know their system best, and much more often than not
provide sound advice.

If you don't have a strong feeling about it, just do what they
say.
-- Tim

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